A common problem in industry occurs when a complex industrial machine (eg. furnace, boiler, etc.) or process having a plurality of series connected relay contacts and switches ceases operation as a result of an intermittent fault. Typically a loose wire or faulty connection in the machine(s) or process causes a contact to temporarily open and close. The opening and closing of the contact often causes a secondary relay such as a safety check relay to trip thereby halting the operation of the machine. Since the original contact fault is only on an intermittent basis, operating or maintenance personnel are required to conduct an extensive check of the machine(s) or process in an effort to determine the cause of the shut-down, prior to re-starting the system. This can result in significant down time and loss of revenue.
While the operating or maintenance personnel are analyzing the machine(s) or process to determine the cause of shut-down, many machine cabinet doors are opened and closed to gain access to various machine components. Such doors are often themselves connected to safety switches. The activation of these additional safety switches can result in additional confusion on the part of maintenance or operating personnel when two or more of such persons are investigating a system simultaneously to determine the source of the shut-down.
Prior art systems are available in the form of warning lights which indicate to a machine operator when a fault or shut-down has occurred. However, the activation of such lights or lamps is also on an intermittent basis so that only switches or contacts which have been permanently opened are indicated by the illumination of the appropriate lights or lamps.